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From 9010d1576e278a4274ad3f4aa15776c28f6ba965 Mon Sep 17 00:00:00 2001
From: NIIBE Yutaka <gniibe@fsij.org>
Date: Wed, 13 Jun 2018 15:28:58 +0900
Subject: [PATCH] ecc: Add blinding for ECDSA.
* cipher/ecc-ecdsa.c (_gcry_ecc_ecdsa_sign): Blind secret D with
randomized nonce B.
--
Reported-by: Keegan Ryan <Keegan.Ryan@nccgroup.trust>
CVE-id: CVE-2018-0495
Upstream-Status: Backport [http://git.gnupg.org/cgi-bin/gitweb.cgi?p=libgcrypt.git;a=commit;h=9010d1576e278a4274ad3f4aa15776c28f6ba965]
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
Signed-off-by: Jagadeesh Krishnanjanappa <jkrishnanjanappa@mvista.com>
---
cipher/ecc-ecdsa.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/cipher/ecc-ecdsa.c b/cipher/ecc-ecdsa.c
index 1484830b..140e8c09 100644
--- a/cipher/ecc-ecdsa.c
+++ b/cipher/ecc-ecdsa.c
@@ -50,6 +50,8 @@ _gcry_ecc_ecdsa_sign (gcry_mpi_t input, ECC_secret_key *skey,
const void *abuf;
unsigned int abits, qbits;
mpi_ec_t ctx;
+ gcry_mpi_t b; /* Random number needed for blinding. */
+ gcry_mpi_t bi; /* multiplicative inverse of B. */
if (DBG_CIPHER)
log_mpidump ("ecdsa sign hash ", input );
@@ -61,6 +63,15 @@ _gcry_ecc_ecdsa_sign (gcry_mpi_t input, ECC_secret_key *skey,
if (rc)
return rc;
+ b = mpi_snew (qbits);
+ bi = mpi_snew (qbits);
+ do
+ {
+ _gcry_mpi_randomize (b, qbits, GCRY_WEAK_RANDOM);
+ mpi_mod (b, b, skey->E.n);
+ }
+ while (!mpi_invm (bi, b, skey->E.n));
+
k = NULL;
dr = mpi_alloc (0);
sum = mpi_alloc (0);
@@ -115,8 +126,11 @@ _gcry_ecc_ecdsa_sign (gcry_mpi_t input, ECC_secret_key *skey,
}
while (!mpi_cmp_ui (r, 0));
- mpi_mulm (dr, skey->d, r, skey->E.n); /* dr = d*r mod n */
- mpi_addm (sum, hash, dr, skey->E.n); /* sum = hash + (d*r) mod n */
+ mpi_mulm (dr, b, skey->d, skey->E.n);
+ mpi_mulm (dr, dr, r, skey->E.n); /* dr = d*r mod n (blinded with b) */
+ mpi_mulm (sum, b, hash, skey->E.n);
+ mpi_addm (sum, sum, dr, skey->E.n); /* sum = hash + (d*r) mod n (blinded with b) */
+ mpi_mulm (sum, bi, sum, skey->E.n); /* undo blinding by b^-1 */
mpi_invm (k_1, k, skey->E.n); /* k_1 = k^(-1) mod n */
mpi_mulm (s, k_1, sum, skey->E.n); /* s = k^(-1)*(hash+(d*r)) mod n */
}
@@ -129,6 +143,8 @@ _gcry_ecc_ecdsa_sign (gcry_mpi_t input, ECC_secret_key *skey,
}
leave:
+ mpi_free (b);
+ mpi_free (bi);
_gcry_mpi_ec_free (ctx);
point_free (&I);
mpi_free (x);
--
2.13.3
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